An exchange-traded fund (ETF) is a basket of assets packaged into a single tradeable instrument. Instead of buying 500 individual stocks to get exposure to the S&P 500, you buy one ETF that holds all of them. It trades like a stock, with a price that moves throughout the day.

How ETFs are structured

Every ETF tracks something. Index ETFs track a specific market index like the S&P 500 or Nasdaq-100. Sector ETFs focus on a single industry, like semiconductors, energy, healthcare, or financials. Commodity ETFs give you exposure to physical assets like gold or oil without needing to own the actual commodity. There are also bond ETFs, international ETFs, and inverse ETFs that move opposite to their benchmark.

The fund manager handles everything behind the scenes, including buying the underlying assets, rebalancing when needed, and maintaining tracking accuracy. You just buy and sell the ETF like any other ticker.

Why traders use ETFs

ETFs solve a practical problem. If you believe the tech sector will outperform next quarter, you don't need to pick which tech company will lead. You buy a tech sector ETF and get diversified exposure in a single trade. One position, one spread, one order.

For portfolio management, ETFs let you build broad market exposure quickly. A trader who wants 60% equities and 40% bonds can build that allocation with two ETFs instead of managing dozens of individual positions.

ETFs also tend to have lower fees than actively managed funds. Most popular ETFs charge expense ratios under 0.10% annually, a fraction of what a mutual fund would charge for similar exposure.

What to watch when trading ETFs

Not all ETFs are equally tradeable. The most popular ones like SPY, QQQ, and IVV trade millions of shares per day with tight spreads. Niche ETFs with lower volume can have wider spreads and more slippage on entry and exit.

Tracking error matters too. An ETF is designed to mirror its benchmark, but small discrepancies appear over time due to fees, rebalancing, and timing. For most major ETFs, tracking error is negligible. For more exotic products, it's worth checking.

The key advantage of ETFs is efficiency. They let you express a market view, whether bullish on tech, bearish on energy, or neutral on the broad market, without the complexity of managing individual positions.